This invention relates to the carbonylation of diolefins. More particularly, it relates to the catalytic carbonylation of diolefins to form esters of polycarboxylic acids under exceptionally mild conditions of temperature and pressure.
A petrochemical process of major economic importance is the conversion of unsaturated hydrocarbons to functionally substituted products such as alcohols, aldehydes, ketones, and carboxylic acids. The hydroformylation of olefins to aldehydes is one such process, and is the first step in the synthesis of oxo alcohols. However, the energy requirements for the oxo process are severe, temperatures above 150.degree. C. and pressures of up to 3000 p.s.i.g. usually being necessary.
The addition of carbon monoxide to olefins (carbonylation) has long been considered in the art to be a highly attractive route to a number of commercially valuable chemical products. In particular, there has been a long-felt need for a convenient method of adding carboxyl groups across a pair of conjugated double bonds in a 1,4-manner efficiently yet under mild conditions of temperature and pressure to form the corresponding .DELTA..sup.3 -adipic acid derivative. A recent survey of prior work in this field appears in Advances in Chemistry, No. 132, "Homogeneous CatalysisII" (American Chemical Society 1974). For example, a facile 1,4-dicarbonylation of butadiene to form an adipic acid precursor would be valuable in the commercial production of linear polyesters and polyamides.
The reaction of carbon monoxide with a variety of cyclic and acyclic olefins at 2-3 atm in methanol in the presence of palladium(II) chloride as catalyst and copper(II) chloride as reoxidant to give, depending on the reaction conditions, various carboxylic acid derivatives, is disclosed in Advances in Chemistry, supra, p.90; J. Am. Chem. Soc., 98, 1810 (1976) and J. Org. Chem., 41, 1504 (1976). For example, linear alpha-olefins give predominantly beta-methoxyesters by trans-addition under neutral conditions and succinic esters by cis-addition in the presence of base: ##STR2## In the synthesis of the above-mentioned beta-methoxyester, a trans-solvopalladation reaction of the olefin is believed to be the first step in the mechanism, followed by carbon monoxide insertions into the metal-palladium sigma bond, as described in J. Am. Chem. Soc., 95, 5062 (1973); J. Am. Chem. Soc., 98, 1806 (1976); J. Am. Chem. Soc., 97, 3282 (1965); J. Am. Chem. Soc., 88, 5135 (1966); J. Am. Chem. Soc., 92, 1274 (1970); J. Am. Chem. Soc., 92, 1798 (1972); J. Am. Chem. Soc., 94, 485 (1972); and Inorg. Nucl. Chem. Letters, 5, 157 (1969). Other reaction solvents with or without added nucleophiles afford beta-substituted carboxylic acid derivatives by the same mechanistic sequence, as described in "Transition Metal Catalyzed Carbonylation of Olefins", Chapter 12 in "The Chemistry of Functional Groups. Supplement A: Double-Bond Functional Groups", S. Patai, Ed. (John Wiley and Sons, Inc., London, 1976). Such solvents (SOH) include alcohols, water, and acetic acid or non-reactive media; nucleophiles (N.sup.-) include chloride, acetate, amines and the like: ##STR3## For example, cyclooctadiene can be catalytically converted, stereo-specifically, to the trans-beta lactone, as described in J. Am. Chem. Soc., 97, 674 (1975); and J. Organometal. Chem., 108, 401 (1976). It is especially noteworthy that this unique transformation to a strained, difficult-to-synthesize class of compounds can be effected at 25.degree. C., under 1-3 atm of carbon monoxide from cheap starting materials: ##STR4##
However, of greater importance as a petrochemical process is the reaction of carbon monoxide with conjugated olefins whereby the product obtained is the result of 1,4-addition of two carboxyl groups across a pair of double bonds. Of major technological significance would be the ability to carry out such processes under mild energy and pressure requirements to form dicarboxylic acid derivatives, e.g. esters.
Accordingly, it is an object of the present invention to provide a process for the carbonylation of olefins to form derivatives of polycarboxylic acids.
Another object is to provide a process for the carbonylation of conjugated diolefins under mild conditions of temperature and pressure to form esters of dicarboxylic acids.
These and other objects as well as a fuller understanding of the invention and the advantages thereof can be had by reference to the following description and claims.